Coated aluminum articles and process and means for producing same



Pae ea Sept. 1, 1925.

. U T STATES 1,551,613 PATENT OFFICE.

AnAnAn PACZ, or EAST cLnvELANn,-on1o, AssmN0n 'ro ALUMINUM COMPANY or AunaIcA, or PITTSBURGH, PENNSYLVANIA, A CORPORATION'OF PENNSYLVANIA.

COATED ALUMINUM ARTICLES AND PROCESS AND MEANS FOR PRODUCING SAME.

No Drawing.

of Ohio, have invented certa n new and useful Improvements in Coated Aluminum Articles and Processes and Means for Broducing Same, of which the following is a full, clear, concise, .and exact description, such as will enable others skilled in the art to which my invention appertains to make This invention relates to the coating of articles of aluminum or aluminum alloys. It is concerned not only with a novel process of coat ing such articles and solutions for practicing this process but is also concerned with the-resulting new and improved products.

QOne of the objects of my invention is to h provide a process for forming on aluminum articles an adherent, hard, non-metallic permanent coating, the color and nature of which may be varied atwill and comprising an oxide or hydroxide ofaluminum.

Another object is to provide a process of forming on an-aluniinum or aluminum alloy article, a coating which is hard, strongly oxidized form.

adherent tothearticle, dense, impervious and capable ofbeing painted,- varnished, enameled or electroplated.

Another'object is toproduce an aluminum or aluminum alloy article having a hard,

non-metallic, permanent, adherent surface coating or film containing aluminum in an ;A further object is to provide a new and lmproved composition of matter for form- 1ng on aluminum or aluminum alloy artlcle,

,an ornamental, aluminous surface coating oi. film which may have a variety of colors and shades.

' Y A still further object is to provide a newand improved com osition o'f-matter capa ble -of reacting with a metallic article containing aluminum to form on the surface thereof a controllably colored coa 'ng composed in part ofaluminum in hxidized form. I

Other objects will appear and'be pointed out hereinaften I have discovered that a surface coating or'filmcontaining aluminum, probably in an oxidized form, may be formed on aluminum-articles, including substantially pure I 7 Application filed March7, 1923. Serial No. 823,542.

aluminum, aluminum base alloys (in which the aluminum predominates) and certain other aluminum alloys in which the aluminum forms a small portion, by subjecting the articles to the action of suitable ammoniacal solutions. I have also discovered that such coatings may be obtained in a simple and inexpensive manner without recourse to complicated mixtures, or solutions difficult to prepare, and without the'use of temperatures above the boiling point of water; and the coatings may be controllably varied over a Wide range as regards thickness, color and roperties. Articles rovi'dedwith coatings having such widely varying properties are naturally capable of many difi'erent uses some of which I will hereinafter describe. I have also discovered that while an ammoniacal solution containing a large quantity of hydroxyl radicals is apparently indispensable for my process, I may advantageously add small quantitles of certain substances, particularly solutions a containing ammonia-soluble metallic salts and ammonium salts for producing the desiredcoatings.

To enable those skilled in the art better sired'and the use to be made of'the coated article. Where a matte, etched or roughened surface is satisfactory as contrasted with a polished, specularly reflecting surface, the cleaning'may be effected. by treat-- ment fof the article first in a caustic solution and then-in a mineral acid. The stren tli of the causticsolution, and the length 0 time it should be used, may both vary somewhat but I prefer to immerse the article in a-hot 5% solution for about one to five minutes,

The article maybe thoroughly washed with water after this cleaning step.

Obviously difi'er'e nt acids will be suitable for the second treatment but I prefer sul- .phuric acid. The stren th of the acid soluof the coating solution the tageous to add to the coating soultion a tion and the length 0 time for which it should be employed may vary depending on the acid and the condition and composition of the article being treated; in the case of sulphuric acid, a 10% solution used for up to about 15 minutes at temperatures up to about the boiling point of water has. been folmd satisfactory even on aluminum alloys containing considerable quantities of silicon. To remove chemical salts, excess acid, and other substances which ma remain on the cleaned article after the acid treatment, the surface thereof should be thoroughly washed with water.

For articles which have smooth polished or s' ecularly reflecting surfaces and particular y where the coated article isto be used asa reflector, and also where the article to be coated is very thin, the caustic solution is preferably replaced by a solution capable of removing grease but not capable of noticeably roughening or corroding the surface. As examples of such substances, carbon tetrachloride or weak nitric acid, with or without a little hydrofluoric acid have been found satisfactory.

The article to be coated having been suitably cleaned is next subjected to the action of a solution containing ammonia, which I will hereinafter designate as a coating solution. This coating solution should contain from about two to twenty per cent by volume of concentrated aqua ammonia,

and preferably is made up by adding one volume of concentrated aqua ammonia to nine volumes of Water. For the most rapid and in many cases the best results the solution is heated to betweenabout 50 C and 100 C., but preferably to about 909 C. A temperature somewhat on either side of this may be employed, but I have observed that the time required for, and thickness and quality of the resulting coating depends upon the temperature of the solution as well as upon the concentration of ammonia. A strong, hot solution acts quickly while. a weaker or cooler solution may require from one to twelve hours or more to form a coating of a similar thickness; firmness and adherence.

. Since the ammonia is rapidly driven out .at high temperatures, it is often advisable to add a little concentrated ammonia to the solution just before the article is introduced so as to insure the presence of suflicient ammonia to form esired coating. Also I findit advansmall amount, say about one percent or more of an ammonium salt, for example-ammonium chloride, sulphate or nitrate, with or without small amounts of salts of alkali metals.

During the early stages of this treatment warms and substantially. impervious to penetration by solutions, smooth, of a low coefficient of friction as compared with metalllc aluminum, and'comprises abase upon. which.

paints, varnishes, enamels or the like may be readily applied and satisfactorily retained.

Such a coating when formed on articles composed of certain aluminum alloys is a sufliciently good electrical conductor to act as an electrode upon which'metals may be electroplated. When, however, sucha coating 'is formed on commercially pure aluminum, especially when the coating solution contains only ammonia, thecoating'acts as an eflicient electrical insulator and two or more of such coated articles may advantageously be emplo ed, for some purposes, as an electrical con enser.

Apparently this coating process has no harmful effect on the physical properties of the article being coated.

I am able at will to color coatings formed by my invention and .to do so dining and without interrupting the coating formation. Certain .colors may be obtained by adding relatively small amounts of metallic salts tocthe coating solution and substantially aluminum article is treated-with a coating solution and to which has been added from about to 2 by Weight of borax.or the equivalent amount of boric acid' in other form, the coating becomes aclear white; if from about to 2 2, by weight of sodium fluorid be added instead of borax,

the coating becomes gray in color.

If small amounts, (say from about 5 to 50 milligrams or more per liter of solution) of one or more metallic salts be addedto the coating solution, I can produce a color, ranging from silver white through all shades of yellow, brown and gray to black, including the various tints of red, blue and green num or alloys upon which they are formed.

When the coating is to be colored in this manner only such metallic salts should be used as are soluble in. ammonia, as for example,

copper, silver, nickel, zinc, cadmium, co b alt, tungsten," molybdenum, vanadium, eifl Combinations of two,or more of such metallic salts often give-'betterresults than when only one is used.

If an aluminum alloy is treated with the coating solution, the resulting coating obtained corresponds to that on pure aluminum as regards most physical roperties but differs in color depending on the color modifying metal or metals in the alloy.

If an alloy containing a substantial amount of silicon is coated, the coating is usually dark colored or even black and pos-' sesses a surface appearance resemblingfinely divided silicon. If an alloy of aluminum with from 1% to 4% of nickel is so treated the resulting color may range from a brass yellow to a dark brown depending on the increasing content of nicke. If the allo;

be of aluminum and tungsten '(e. g. aluminum95 to 99%, tungsten 5 to 1%) the coating varies from a silver white at 1% of tung- .sten to a .light brass yellow color. at the higher tungsten content. If the alloy be of aluminum and silver, the color verges on yellow though with a golden cast with about 5 of silver, and becomes darker and more prominent up to a very strong and bright red, as the silver content is increased. If the alloy-be of aluminum and iron the color obtained is a light gray with about 1% of iron which progressively darkens upto 4% or 5% although never becoming very dark. Other aluminum base alloys similarly treated afi'ord characteristic coatings, for example, those containing copper, cobalt, manganese, chromium, moly denum, uranium, zirconium, thorium, cerium, zinc. If an alloy containing about 88% zinc, 2% copper and 10% aluminum be treated with the coating solution, the resulting coating is nearly'black. i

If commercially pure aluminum is subjected to the coating solution in. the pres- .ence of a metallic article such as a piece of silver ,or nickel, the resulting coating differs somewhat -from the coating formed when. the same metal is absent. 1

For specular reflection, such'a's is desired in reflectors for searbh lights and automobile headlights, for example, it is desirable in- .stead of pickling to firstpolishby the ordinary means andthen clean the aluminum articles with a substance such as carbon tetrachloride which will not destroy the polished surface thereof. Such articles when coated 1n accordance with my invention will be found to reflect light substantially without diffusing the same.

Although in the foregoing description I have disclosed the composition of several solutions which may be used for carrying out my improved process and producing on I aluminum or aluminum alloy articles the new and improved coatings, I do not wish to be understood as having included all of the various compositions which could be so employed. The presence of considerable amounts of ammonia is essential regardless of the color, thickness or physical properties of the coating desired. ,This application is a continuation in part of my two prior applications which are identified as follows :Serial No. 559,465, filed May 8} 1922; Serial No. 549,204, filed April 3, 1922. It will be understood that my invention in any of itsaspects is not to be limited to What has been described since various alterations or modifications may be made by-those skilled in the art without involving invention or departing from the scope of my invention.

It will be seen that my invention may be practiced by dipping or immersing the article to be coated in a suitable solution without the. application of electrical energy from anexternal source, or the subsequent employment of high temperatures.

In the appended claims the term aluminum article is intended to include also aluminumalloy articles as herein described.

Having thus disclosed my improved process of coating aluminum or aluminum alloy articles in considerable detail together with various compositions of matter or solutions which may be employed in carrying outmy process and certain of the products resulting fromthe process together with their properties and uses, what I desire to secure by Letters Patent is defined in what is claimed. What is claimed 1. The process of producing an adherent, non-metallic, controllably colored coating upon an aluminum article which comprises the step of immersing the said article, without the application of external electrical energy, in a hot-ammonia solution containing an ammonium salt and small amounts of one or moremetallicsalts in solution.

2.The rocess of coating'an aluminum article which comprises cleaning the surface oi the said article, and immersing the article in an ammoniasolution containing a small proportion of an ammoniunisalt and a color modifying substance includingsilveig 126 without the application of monia, nine parts of water, and from about article in a hot ammonia solution containing a small proportion of an ammonium salt and a color modifying substance including silver until acolored coating has been formed thereon.

4. The process of coating an aluminum article which comprises cleaning the surface of the said article, and immersing the article in an ammonia solution containing a small pro-portion of an ammonium salt and a small amount of color modifying ammonia soluble salt including silver until a colored coating has been formed.

5. As a new composition of matter, a solution for coating aluminum articles which comprises a substantial proportion of am monia, a small proportion of an ammonium salt, and a small amount of an ammonia soluble silver salt.

6. The process of producing a colored non-metallic coating on an aluminum article which comprises cleaning the surface. of the said article, forming a. solution of approximately one part of concentrated aqua-ammonia, nine parts of Water and from about one tothree parts by weight of an ammonium salt, heating the solution, adding thereto a small amount of an ammoniacal solution of a metallic salt, and immersing therein the said article until a colored coatin" is formed thereon.

r. The process ofproducing a colored non-metallic coating on-an aluminum article which comprises cleaning the surface of the saidarticle, forming a solution of approximately one part of concentrated aqua-am monia, nine parts of water and from about one to three parts by weight of an ammonium salt, heating the solution, and im; mersing therein the said article until a colored coating is formed thereon;

i e process of producing a colored non-metallic coating on an aluminum article which comprises cleaning'the surface of the said article, forming a solution of approximately one part of concentrated aqua-amone to three inonium salt, theretoa small amount of solution of a metallic jsalt, and immersing parts by weight of an amtherein the said article .until a colored coat-..,

ing is formed thereon."

9. The process .of producing a colored non-metalllc coating on an aluminum article which comprises cleaning the surface of the said article, forming a solution ofapproximately one part of concentrated aqua amnionia, nine parts of water, and from about one to three parts by weight of an ing thereto a eating the solution, adding an ammoniacalsigned my meters ammonium salt, heating the solution up to about the boiling point of water, adding thereto a small amount of an ammoniacal solution for use incoating an aluminum article which comprises ammonia contain" ing an appreciable amount of an ammonium salt and a small amount of an ammoniasoluble silver salt.

11. As a new composition of matter a solution for coating an aluminum article comprising ammoniacontainnig an appre ciable amount of a fluoride of an alkali metal.

12. As a newcomposition of matter, a solution for coating aluminum articles which comprises a substantial proportion of ammonia, a small proportion of an ammonium salt, and a small amount of one or more ammonia-soluble metallic salts, including silver.

13. As a new composition of matter, a solution for coating aluminum articles which comprises a substantial proportion of ammonia, a small proportion of an ammonium salt, a small amount of an ammonia-soluble silver salt, and a small amount of an ammonia-soluble, color modifying salt.

14. ,A process of producing a colored nonmetallic coating on an aluminum article which comprises cleaning the surface of the said article, forming a solution of approximately one part of concentrated aqua -a-mmonia, nine arts of water, and about one part by weig t of an ammonium salt, addsmall amount of an ammoniacal solution of a silver salt, and immersing therein the said article until a colored coating is formed thereon.

15. The process of'producing a colored non-metallic coating on an aluminum article which comprises cleaning the surface of the .said article, forming a solution of approxitrated aqua-amand one or more other colored modifiying' metals, and immersing therein the sai article until a colored coating is formed thereon.

In avitness whereof, I have hereunto name this 6th day of March,

PA'CZ. 

